This invention relates to traveling wave tube amplifiers, and, more particularly, to the method of fabricating the barrel of traveling wave tubes and of supporting the traveling wave tube circuit assembly within the barrel.
Traveling wave tubes are used to amplify signals in microwave systems. For example, traveling wave tubes may be provided in satellite communications systems to amplify the signals received from earth before their retransmission back to earth.
The traveling wave tube generally includes an input coupling element, an output coupling element, and a traveling wave circuit therebetween. The traveling wave circuit consists of a wire helix or other slow wave structure interacting with an electron beam that is confined within a barrel. The barrel provides a vacuum envelope and support structure for the traveling wave tube circuit. The barrel is typically made of a thermally conductive metal such as annealed copper, although other materials may be used. The wire helix is supported by dielectric rods from the inner wall of the bore of the barrel. The dielectric rods serve to position the wire helix, and also to conduct heat from the wire helix to the barrel, where the heat is dissipated. A properly controlled electron current flowing through the interior passage of the helix transfers energy to the microwave signal flowing in the wire helix, thereby amplifying the microwave signal.
In a typical manufacturing operation, the inner bore of the barrel is sized to a cylindrical shape within close tolerances. Sizing may be accomplished by honing, reaming, or drilling. The barrel is thereafter heated to elevated temperature to expand it radially, a traveling wave circuit assembly including the dielectric rods and the wire helix is placed into the barrel, and the barrel is cooled to shrink it into contact with the dielectric rods. The traveling wave circuit is supported from the barrel by a tight interference fit.
While operable and widely used, this technique requires a large number of steps and careful process control to prevent contamination of the final assembly by chips, powder, chemicals and the like produced or used during the sizing operation. The sizing operation is conducted in a machine shop, and the assembly is performed in a clean room. The sized barrel must be moved between the various locations, inspected multiple times, and carefully cleaned each time it is to enter the clean room. All of these steps are time consuming and lead to a substantially increased cost of manufacture.
There is a need for an improved approach to the fabrication and assembly of traveling wave tubes. The present invention fulfills this need, and further provides related advantages.